Electric motors consume more than half of all electrical energy used in most countries. Currently, the majority of all motors used are induction motors. Induction motors provide simple and reliable operation and have relatively low manufacturing cost. Unfortunately, induction motors do not provide the highest efficiency.
Some applications of motors and generators run continuously or near continuously. In such applications, the annual electricity consumption costs can be several times greater than the acquisition cost of the motor. Increasing the efficiency of motors used for these applications could provide significant economic benefit.
Another type of motor that can provide higher efficiency than induction motors is the brushless permanent magnet motor. Because the field flux in permanent magnet motors is produced by magnets instead of electrically excited windings as in induction motors, they can operate more efficiently. Unfortunately, conventional brushless permanent magnet motors are more expensive than induction motors. They also do not always provide a great enough increase in efficiency and energy savings to justify the increased cost and make them an economically viable alternative, except where the functional benefits of brushless permanent magnet motor necessitate their use.
One way to increase the efficiency of brushless permanent magnet motors is to eliminate eddy current and hysteresis losses occurring in laminations by eliminating the use of electrical laminations in construction. In such motors, the armature comprises windings with an air core instead of being wound into slots in the laminations. This type of construction also provides the benefits of reduced winding inductance for higher speed operation. As such, these types of motors are small and typically used in cameras, dental drills, flywheel energy storage systems and specialized application servomotors. Despite their potential for increased efficiency, air core brushless motors have heat generation that is difficult to remove without incurring significant additional losses or substantial costs. The heat generation, if not effectively removed, can limit the duty cycle of the motor through over heating. Accordingly, a brushless air core permanent magnet motor with low loss cooling is desired.